Endoscopes are slender light transmitting glass lined metal rods used during operations to permit the doctor to see within the site of the operation, such as during an arthroscopic procedure. Endoscopes designed and dimensioned for use in the joints of the body are referred to as arthroscopes. Since arthroscopes are very expensive, typically many thousands of dollars, and are very fragile, they are carefully protected by an outer cannula. A cannula is a tubular sleeve like member that closely surrounds the arthroscope, mitigating against breakage, during introduction into the wound or during use.
During an operation, it is necessary in order for the surgeon to see within the operating space for fluid to be introduced into the site of the operation to both inflate the site of the operation and to make sure that clear fluid is in the site. This is typically achieved by having an inlet at the proximate end of the cannula which forces sterile water through the space between the inside wall of the cannula and the outer wall of the arthroscope and into the wound. If the fluid becomes cloudy, then the inlet is closed and suction can be applied to an outlet at the proximate end to withdraw the cloudy fluid.
However, because of the close tolerances required to support the arthroscope, the volumetric space between the cannula wall and the arthroscope is very limited, and can not be arbitrarily increased. If too much clearance is provided, then the support to the arthroscope may be insufficient to prevent its breakage. Further, the size of the cannula can not be substantially increased due to the inability to maneuver a substantially larger instrument into the operation site. Thus, when substantial amounts of fluid must be introduced into the operation site and insufficient flow is obtainable through the arthroscope and cannula device, it is then necessary to introduce the fluid through additional incisions made into the site. While this is undesirable in any case, in some procedures, such as an arthroscopic procedure on the shoulder, the additional incisions could cause real damage to the rotator cuff. At the same time, the presence of additional tubes cause the procedure itself to be more difficult to perform. Thus, the design of the prior cannula represented a compromise between the desire to adequately support the arthroscope and the desire to have fluid flow.